Subject Code : 06CV64 PART A UNIT 1
Internal Assessment Marks : 25
1. SUBSURFACE EXPLORATION 1.1 Importance, Exploration Program 1.2 Methods of exploration, Boring, Sounding Tests, Geophysical methods – Electrical resistivity and Seismic refraction methods 1.3 Types of samples – Undisturbed, Disturbed and Representative samples 1.4 Samplers, Sample disturbance, Area ratio, Recovery ratio, Clearance 1.5 Stabilization of bore holes 1.6 Typical boring log 1.7 Number and depth of boring for various Civil Engineering structures 1.8 Soil exploration report (7 Hours)
Chapter -1 SUBSURFACE EXPLORATION
Earthwork forms the largest activity of a Civil Engineer. It is well understood that irrespective of the type of civil engineering structure on earth – • It has to be rested either in soil (e.g., foundations) • Rested on soil (e.g., pavements) or • The structure is itself constructed making use of soil (e.g., Earthen dams). This implies that a better knowledge of the spatial variation of the soils encountered is essential. Therefore, before construction of any civil engineering work a thorough investigation of the site is essential. Site investigations constitute an essential and important engineering program which, while guiding in assessing the general suitability of the site for the proposed works, enables the engineer to prepare an adequate and economic design and to foresee and provide against difficulties that may arise during the construction phase. Site investigations are equally necessary in reporting upon the safety or causes of failures of existing works or in examining the suitability and availability of construction materials. Site investigation refers to the methodology of determining surface and subsurface features of the proposed area. Information on surface conditions is necessary for planning the accessibility of site, for deciding the disposal of removed material (particularly in urban areas), for removal of surface water in water logged areas, for movement of construction equipment, and other factors that could affect construction procedures. Information on subsurface conditions is more critical requirement in planning and designing the foundations of structures, dewatering systems, shoring or bracing of excavations, the materials of construction and site improvement methods.
1.2 Soil Exploration
The knowledge of subsoil conditions at a site is a prerequisite for safe and economical design of substructure elements. The field and laboratory studies carried out for obtaining the necessary information about the surface and subsurface features of the proposed area including the position of the ground water table, are termed as soil exploration or site investigation.
1.3 Objectives of soil exploration program
The information from soil investigations will enable a Civil engineer to plan, decide, design, and execute a construction project. Soil investigations are done to obtain the information that is useful for one or more of the following purposes. 1. To know the geological condition of rock and soil formation. 2. To establish the groundwater levels and determine the properties of water. 3. To select the type and depth of foundation for proposed structure 4. To determine the bearing capacity of the site. 5. To estimate the probable maximum and differential settlements. 6. To predict the lateral earth pressure against retaining walls and abutments. 7. To select suitable construction techniques 8. To predict and to solve potential foundation problems 9. To ascertain the suitability of the soil as a construction material. 10. To determine soil properties required for design 11. Establish procedures for soil improvement to suit design purpose 12. To investigate the safety of existing structures and to suggest the remedial measures. 13. To observe the soil the soil performance after construction. 14. To locate suitable transportation routes.